An antenna for mobile communication is a device that transmits and receives date by mutually converting electric power and radio frequency energy, and recently, studies on improving the transmission quality and implementing miniaturization of a mobile device have been actively conducted in order to satisfy rapidly increasing amounts of data communication.
An operating frequency band for securing the quality of transmitting and receiving data is planned to increase from 0.8 to 2.1 GHz to 5 GHz by 2020. Accordingly, it is expected that the demand for microstrip antenna devices available in a wide bandwidth including super high frequency (SHF) is increased. Due to advantages in that the microstrip antenna is lightweight, easily manufactured, and suitable for mass production, and easily implements an array antenna, the microstrip antenna has been currently used in various fields over the radio frequency (RF), starting from the application to the spaceship field in the early 1970s. In particular, when a high permittivity and high permeability substrate, which replaces a printed circuit board (PCB) and a dielectric material, is used, the substrate for use in a mobile phone operating in a high frequency band is used in various cases.
In order to make a wireless transmission magnetic device small, enhance the performance of the wireless transmission magnetic device, and increase the operating frequency stability, soft magnetic materials having excellent high frequency characteristics are required. Further, due to the development of information communication, various bands and a broad bandwidth need to be simultaneously used instead of an existing single band in a high frequency region, and as the device becomes smaller, characteristics of the soft magnetic material are also required at a higher level. The soft magnetic material basically needs to have excellent permeability and saturation magnetization, high electric resistance and low coercive force characteristics and low eddy current loss characteristics are required. Since a metal-based soft magnetic material such as Fe, Co, Ni, or permalloy (FexNi1−x (X is a real number less than 1)) has a low electric resistance, the eddy current loss is high, and as a result, there is a problem in that the permeability is sharply decreased in a high frequency band in the GHz region. Accordingly, for the application in a high frequency region, the permeability may be maintained only when the material needs to decrease the eddy current loss by having a high electric resistance. Due to the disadvantages of the metal-based soft magnetic material, a ferrite (MFe2O4)-based material having high electric resistance in a high frequency region is usually used. Currently, a ferrite-based material having high resistivity has been usually used in antenna for mobile communication operating in a band between several MHz and 1 GHz, but the ferrite-based material has a limitation in being used in a frequency band of 1 GHz or more because the volume is increased due to the small saturation magnetization value.